1. Field of the Invention
Apparatuses consistent with the present invention relate to an illumination system for a flat panel display device in which light, incident on a light guide plate from a light source disposed at a side of the illumination system, is polarized to be emitted to a flat panel display device.
2. Description of the Related Art
Typical flat panel display devices include light emission type flat panel display devices and light receiving type flat panel display devices. Liquid crystal displays (LCDs), which are a type of flat panel displays, are light receiving type displays that are not self-luminescent but which form an image using incident light from an external source. Thus, an external light source, for example, a backlight system, is installed on a rear side of an LCD so as to provide light for an image. Backlight systems for LCDs are generally either direct light emitting type backlight systems or edge light emitting type backlight systems.
In edge light emitting type backlight systems, a linear light source is installed at an end of an LCD panel, and a light guide plate uniformly guides light emitted from the light source to a rear side of the LCD panel.
However, since the light emitted through the light guide plate in a conventional backlight system is unpolarized, it cannot be used in an LCD and needs to be polarized using a polarization unit. In this procedure, a considerable amount of the light energy is lost and energy efficiency is reduced. Moreover, the lost light energy is changed into thermal energy, causing problems such as overheating. Accordingly, there is a need for a more efficient illumination system which provides polarized light.
Recently, illumination systems have been suggested in which light of one polarization is emitted to a light guide and light of another polarization is recycled, thereby improving efficiency, as disclosed in U.S. Pat. Nos. 5,845,035 and 5,808,709.
In an illumination system disclosed in U.S. Pat. No. 5,845,035, a refractive index difference at an interface between an optically isotropic layer and an optically anisotropic layer causes the total reflection of light of one polarization, thereby dividing incident light into polarization component. However, since the refractive index difference at the interface is not large enough, as discussed in U.S. Pat. No. 5,808,709, a collimation unit is required. The collimation unit causes light to be incident on the light guide at an angle at which the light will be totally reflected. However, the collimation unit may be insufficient, causing inefficient polarization separation.